1. Field of the Invention
The present invention relates to a liquid crystal display device and a fabrication method thereof and, particularly, to an IPS (In-Plane Switching) mode active matrix type liquid crystal display device and a fabrication method thereof.
2. Description of the Prior Art
An active matrix type liquid crystal display device (referred to as xe2x80x9cAMLCDxe2x80x9d, hereinafter), which uses TFT""s (Thin Film Transistors) as pixel switching elements, can provide a high image quality and has been used as a display device of a portable type computer and, particularly, as a monitor of a compact desk-top computer recently.
The AMLCD is roughly classified to a type in which a display is performed by rotating a direction of molecular axis of oriented liquid crystal molecule, which is called xe2x80x9cdirectorxe2x80x9d, in a plane orthogonal to a substrate thereof and a type in which a display is performed by rotating the director in a plane parallel to the substrate.
A liquid crystal display device of the TN (Twisted Nematic) mode is a typical example of the former type and that of the IPS (In-Plane Switching) mode is a typical example of the latter type.
Since, in the AMLCD of the IPS mode, a user basically looks liquid crystal molecules in only shorter axis direction even when a view point is moved, there is no dependency of the xe2x80x9crisingxe2x80x9d of liquid crystal molecule on a viewing angle and so it is possible to achieve the viewing angle, which is wider than that achievable in the TN mode liquid crystal display device.
In general, when a liquid crystal display device is manufactured, a patterning on a substrate is performed by photolithography using a photo mask.
Since, when the size of a liquid crystal panel becomes larger, the size of the photo mask for transferring a pattern of a liquid crystal panel onto a whole surface of the substrate becomes larger, the cost of the photo mask becomes very high. Therefore, in order to reduce the manufacturing cost, it is usual that repeated patterns to be formed in respective display regions are formed by dividing the whole display region to a plurality of sub regions and exposing the sub regions one by one with using a single small photo mask for one pattern. This technique is generally referred to as xe2x80x9cstepper exposurexe2x80x9d.
However, since the stepper exposure is performed in the display region within the substrate, it is required, in laminating patterned layers in the display region, to precisely pattern an underlying layer in a vertical direction in every shot and to make an error of overlapped area between adjacent exposure shots as small as possible in a horizontal direction in every exposing shot.
When the overlapped area between the adjacent exposure shots is large, the quality of formed pattern becomes different between the exposure shots, resulting in a display defect called unevenness of division.
On the other hand, the IPS mode AMLCD has the merit of wide viewing angle while has a demerit of small area of a aperture of a pixel region. Therefore, the demand of a technique for increasing the area of the aperture has become prosperous recently.
An example of the IPS mode liquid crystal display device is disclosed in JP H07-036058 A (referred to as xe2x80x9cprior art 1xe2x80x9d, hereinafter).
The IPS mode liquid crystal display device disclosed in the prior art 1 is constructed with a TFT array substrate, scanning lines formed on the substrate, which is formed firstly, a common electrode formed in a metal layer, which is in the same layer of the scanning lines, signal lines (referred to as xe2x80x9cdata linesxe2x80x9d, hereinafter) formed between the common electrode and an insulating film and pixel electrodes formed in the same layer of the data lines.
Another example of the IPS mode liquid crystal display device is disclosed in U.S. Pat. No. 6,069,678 (corresponding to JP H10-186407 A and referred to as xe2x80x9cprior art 2xe2x80x9d, hereinafter). In one embodiment of the prior art 2, a common electrode is formed in an uppermost layer in lieu of the same layer as the initially formed scanning lines.
Since, in the latter case, it becomes possible to shield electric field generated by the data lines by the common electrode and to widen an effective display region of the pixels, it becomes possible to improve the aperture ratio of the pixel and, hence, the light utilization efficiency.
It is usual that, when a large area LCD is to be exposed by using a stepper, a very high positional accuracy is required between the exposure shots.
Describing this with reference to the stepper exposure, a pattern exposure for a substrate is performed by dividing the pattern as shown in FIG. 1. Assuming that the size of a transparent insulating substrate is constituted with zones 37Z, zones 1Z to 20Z arranged in a peripheral portion form a peripheral terminal portion for inputting voltages to a display region and the display region as a liquid crystal display is formed by zones 21Z to 36Z within an area defined by a thick solid line.
For example, FIG. 2 shows a case where only the exposure shot in the zone 21Z is deviated rightward with respect to a gate layer. FIG. 3A shows an ideally arranged pattern of a layout in the vicinity of a unit TFT element. As shown in FIG. 3A, an interlayer insulating film is formed on a scanning line 28 forming a first wiring layer and a common electrode wiring portion 26a and, on the interlayer insulating film, data lines 24 forming a second wiring layer and a pixel auxiliary electrode 35 are formed. In the TFT region, an amorphous silicon layer 29 is formed on the scanning line 28 and a drain electrode 30a connected to the data line 24 and a source electrode 30b connected to the pixel auxiliary electrode 35 are formed on the amorphous silicon layer 29.
FIG. 3B shows a case where the pattern of the data line, the drain electrode and the pixel auxiliary electrode is deviated in the rightward direction. In FIG. 3B, when the exposure shot of the zone 21Z is deviated rightward with respect to the scanning line 28 (gate line), areas of the drain electrode and the source electrode, which are overlapped with the amorphous silicon layer 29 are reduced. Therefore, write characteristics and holding characteristics of the TFT, which is formed by the exposure shot of the zone 21Z, with respect to voltage applied to liquid crystal of the TFT are varied. Therefore, a display state becomes uneven since only the region in which the exposure shots are deviated becomes dark as shown in FIG. 5, comparing with a uniform display state of a liquid crystal display device having no overlapping deviation between adjacent exposure shots shown in FIG. 4.
When the data line 24 and the pixel auxiliary electrode 35 on the gate layer (scanning line 28) are deviated with respect to the gate layer by various amounts between adjacent exposure shots, the deviation is observed as unevenness of display, which is looked as unevenness of division such as shown in FIG. 6.
In order to achieve such high precision alignment, the second (second wiring layer) and subsequent exposures to be performed subsequent to an exposure of the first layer (first wiring layer), which is performed on absolute position with high precision, must be performed as mentioned below.
Firstly, a test exposure is performed by detecting an alignment marker formed in the first layer and, on the basis of the detected alignment marker as a reference, programming the exposure such that a designed overlapping with the pattern of the first layer is obtained.
Secondly, it is necessary to measure the positional relation of the resist pattern of the second layer to the pattern of the first layer by a fine distance measuring device, detect a deviation of the resist pattern of the first layer from an optimal position on the basis of the measurement and feeding back the detected deviation to the exposure program to thereby make the second exposure shot to the optimal position, and so on.
In the prior art 1 mentioned above, there is the common electrode in the first layer, which extends in a longitudinal direction of the data line of the second layer. Therefore, it is possible to perform the alignment in a lateral direction precisely by using a plurality of common electrodes as references in position measurement in the lateral direction by means of the fine distance measuring device.
Further, it is possible to perform the alignment in a longitudinal direction precisely by using a scanning line in the first layer, which extends laterally, or a wiring for the common electrode for applying a potential to the common electrode as a reference in position measurement in the longitudinal direction by means of the fine distance measuring device.
However, when there is no pattern such as the pattern of the common electrode extending in the extending direction of the data line in the first layer as in the case of the prior art 2, there is no reference for the lateral position measurement by means of the fine distance measuring device. Therefore, there is a problem that it is impossible to precisely perform the lateral alignment and unevenness of division tends to occur.
The present invention was made in view of these problems and an object of the present invention is to provide an active matrix type liquid crystal display device, which can excludes the problems of the prior art display device.
Another object of the present invention is to provide a manufacturing method for manufacturing the active matrix type liquid crystal display device.
In order to achieve the above objects, the present invention is featured by that a region having sides extending in a wiring direction of a second wiring layer is formed of a material forming a first wiring layer (underlying wiring layer) in the same time as the time in which the first wiring layer is formed.
According to the present invention, in an IPS mode active matrix type liquid crystal display device having a pair of substrates sandwiching a liquid crystal layer therebetween, a first electrically conductive layer, which constitutes scanning lines each extending over a plurality of pixel regions and a common electrode wiring, is formed on one of the substrate pair, which is an active element side substrate on which switching elements such as TFT""s are formed. Positioning reference pattern regions each extending in a direction crossing an extending direction of the scanning lines are formed in the first conductive layer. Further, a plurality of switching elements are formed on the active element substrate correspondingly to a plurality of pixel regions related to the scanning lines. A second electrically conductive layer constituting data lines each extending over a plurality of pixel regions related to the plurality of the switching elements is formed simultaneously with the formation of the electrodes of the switching elements and the extending direction of the data line is positioned such that it coincident with an extending direction of the positioning reference pattern regions. Further, a third electrically conductive layer constituting the pixel electrodes and the common electrode is formed on the side of the uppermost layer (close to the liquid crystal layer) and the pixel electrodes are electrically connected to the respective switching elements through contact-holes.
In a preferred embodiment of the IPS mode active matrix type liquid crystal display device according to the present invention, the common electrode is formed of a transparent electrode material and the data lines except portions thereof in the vicinity of the scanning lines are positioned within width of the common electrode. The positioning reference pattern region has at least one of a protruded portion and a recessed portion provided in at least one of a portion of the common electrode wiring and a portion of the scanning line.
In another preferred embodiment, the common electrode and the pixel electrodes are formed of the same material and the common electrode is electrically connected to the common electrode wiring through contact-holes provided in an insulating layer between the first electrically conductive layer and the third electrically conductive layer in every pixel region.
In a further preferred embodiment, a black matrix layer having width smaller than the width of the common electrode covering the data line is formed in a position opposing to the data line on the opposing substrate opposing the active element substrate such that a light shielding film does not exist between the common electrode covering the data line and the pixel electrode adjacent to the common electrode in a plan view.
In another preferred embodiment of the present invention, when the positioning reference patter region is the protruded or recessed portion, the positioning reference pattern regions are arranged on both sides of the data line.
The width of the protruded or recessed portion as the positioning reference pattern region in a direction orthogonal to the data line is preferably not smaller than 2 xcexcm and not larger than 10 xcexcm. By setting the width of the protruded or recessed portion in the above mentioned range, it is possible to perform the fine distance measurement with high precision without reducing the aperture ratio.
Particularly, a length of the protruded portion is preferably not smaller than 5 xcexcm and not larger than the length of the pixel aperture. In such case, it is possible to stably perform the fine distance measurement with high precision.
Further, in a preferred embodiment of the IPS mode active matrix type liquid crystal display device according to the present invention, the switching element is a thin film transistor and a semiconductor layer region for thin film transistors is formed on a first insulating layer formed on the scanning lines as gate electrodes thereof. In this embodiment, a source electrode and a drain electrode of the thin film transistor in the semiconductor layer are formed by a second electrically conductive layer and one of the source and drain electrodes and the other electrodes are electrically connected to the data lines and the pixel electrodes, respectively.
Particularly, the above mentioned IPS mode active matrix liquid crystal display device mentioned above further includes a color layer and the black matrix layer formed on the second substrate. In the liquid crystal display device, a reference potential is applied to the common electrode, the common electrode wiring and the scanning line are formed of the same material in the same step and the gate electrode, the drain electrode, the source electrode and the common electrode are electrically connected to the scanning line, the data line, the pixel electrode and the common electrode wiring, respectively. a display is performed by rotating molecular axis of the liquid crystal layer in a plane parallel to a main surface of the first substrate by electric field applied substantially in parallel to the main surface, the data line except a portion thereof in the vicinity of the scanning line is completely covered by the common electrode by interposing an insulating layer therebetween, the common electrodes are connected to the common electrode wiring through contact-holes provided in the respective pixel regions, at least one of the common electrode wiring and the scanning line has at least one of a protruded portion and a recessed portion extending in the extending direction of the data line in every pixel region, the width of the black matrix arranged in the position opposing to the data line in the region in which the data line is completely covered by the common electrode is smaller than the width of the common electrode covering the data line and there is no light shielding film between the common electrode covering the data line and the pixel electrodes adjacent thereto.
In another embodiment of the present invention, the positioning reference patterns are arranged in the vicinity of the data line as floating regions electrically separated from the scanning line and the common electrode wiring.
In the latter construction having the floating regions, at least one of the floating regions may be formed in only pixel regions of any one of red, green and blue colors. With such arrangement of the floating regions in the pixels of only one of R, G and B colors, it is possible to stably perform the fine distance measurement with high precision. The aperture ratio can be further improved by reducing the number of the floating regions.
At least one of the floating regions may be formed at intervals of several pixel regions. With such arrangement of the floating regions, it is possible to highly precisely perform the fine distance measurement and the aperture ratio can be further improved by reducing the number of the floating regions.
At least one of the floating regions is arranged immediately below the data line with the insulating film interposed therebetween. By arranging the floating region immediately below the data line, it is possible to form a pattern with which the fine distance measurement can be stably performed without reducing the aperture ratio. Further, by providing the floating regions, the data line has no capacitive load and so it is possible to prevent signal delay.
In a method for manufacturing the above mentioned IPS mode active matrix type liquid crystal display device, according to the present invention, in which the pattern formation of at least the display region is performed by the stepper exposure using a divided photo mask, an exposure correction between the divided exposures in performing a patterning of a new layer of laminated layers in which the common electrode wiring is formed by photolithography is performed by finely measuring a relative position of the photo mask to the layer in which the common electrode wiring is formed by means of the positioning reference pattern region.
According to a more preferred embodiment of the present invention, an IPS mode active matrix type liquid crystal display device including at least an active element substrate, an opposing substrate and a liquid crystal layer held between the active element substrate and the opposing substrate, is provided, wherein the opposing substrate includes a color layer and a black matrix layer and the active element substrate includes TFT""s each including a gate electrode, a drain electrode and a source electrode, pixel electrodes corresponding to pixels to be displayed, a common electrode supplied with a reference potential, a data line, a scanning line and a common electrode wiring, the common electrode wiring and the scanning line are formed of the same material in the same step, the gate electrode, the drain electrode and the source electrode of the TFT are electrically connected to the scanning line, the data line and the pixel electrode, respectively, and a display is performed by rotating molecular axis of the liquid crystal layer in a plane parallel to a main surface of the active element substrate by electric field applied between the pixel electrode and the common electrode substantially in parallel to the main surface of the active element substrate, the common electrode is formed of a transparent electrode material on a layer closer to the liquid crystal layer than the data line, the data line except a portion thereof in the vicinity of the scanning line is sandwiched between the insulating films and completely covered by the common electrode, the common electrodes are connected to the common electrode wiring through contact-holes provided in the respective pixel regions, the width of the black matrix arranged in the position opposing to the data line in the region including protruded or recessed portions formed by a portion of the common electrode wiring or the scanning line and extending in the extending direction of the data line in every pixel region and completely covered by the common electrode is smaller than the width of the common electrode covering the data line and there is no light shielding film between the common electrode covering the data line and the pixel electrodes adjacent thereto.
According to another embodiment of the present invention, an IPS mode active matrix type liquid crystal display device including at least an active element substrate, an opposing substrate and a liquid crystal layer held between the active element substrate and the opposing substrate, is provided, wherein the opposing substrate includes a color layer and a black matrix layer, the active element substrate includes TFT""s each including a gate electrode, a drain electrode and a source electrode, pixel electrodes corresponding to pixels to be displayed, a common electrode supplied with a reference potential, a data line, a scanning line and a common electrode wiring, the common electrode wiring and the scanning line are formed of the same material in the same step, the gate electrode, the drain electrode, the source electrode and the common electrode are electrically connected to the scanning line, the data line, the pixel electrode and the common electrode wiring, respectively, and a display is performed by rotating molecular axis of the liquid crystal layer in a plane parallel to a main surface of the active element substrate by electric field applied between the pixel electrode and the common electrode substantially in parallel to the main surface of the active element substrate, the common electrode is formed of a transparent electrode material on a layer closer to the liquid crystal layer than the data line, the data line except a portion thereof in the vicinity of the scanning line is completely covered by the common electrode with an insulating film sandwiched therebetween, the common electrodes are connected to the common electrode wiring through contact-holes provided in the respective pixels, a pattern extending in the extending direction of the data line every unit element and formed of the same film as that of the common electrode wiring and the scanning line is arranged in the vicinity of the data line or in the vicinity of the pattern formed by the same layer as that of the data line, the pattern formed by the same film as that of the common electrode wiring and the scanning line is electrically floating, the width of the black matrix arranged in the position opposing to the data line in the region in which the data line is completely covered by the common electrode is smaller than the width of the common electrode covering the data line and there is no light shield film between the common electrode covering the data line and the pixel electrodes adjacent thereto.
Since, in such liquid crystal display device, the pattern extending in the longitudinal direction of the data line is formed in the same layer as that including the initially formed scanning line and the common electrode wiring, it becomes possible to precisely perform the alignment for the second and subsequent layers by using the pattern as the reference for the fine distance measurement to thereby obtain the IPS mode liquid crystal display device having high aperture ratio without divisional variation, which is caused by the stepper exposure.
Further, the present invention provides an IPS mode liquid crystal display device featured by that protruded or recessed portions formed by a portion of the common electrode wiring or a portion of the scanning line are arranged such that the data line is put between the protruded or recessed portions. By forming the protruded or recessed portions such that the data line is put between them, it is possible to precisely perform the fine distance measurement between the layer (the layer of the data line) in which the source and/or drain electrode of the TFT is formed and the layer in which the scanning line is formed to thereby perform the alignment between them more precisely.
Further, according to the present invention, an IPS mode liquid crystal display device featured by that the pattern formed in the same layer as that of the common electrode wiring and the scanning line extends in the extending direction of the data line and has a width in a direction perpendicular to the data line extending direction is in a range from 2 xcexcm or more to 10 xcexcm or less is provided. By setting the width of the pattern as above, it is possible to perform the fine distance measurement with high precision without reducing the aperture ratio.
Further, according to the present invention, an IPS mode liquid crystal display device featured by that the pattern formed in the same layer as that of the common electrode wiring and the scanning line extends in the extending direction of the data line and has a length in a direction parallel to the data line is not smaller than 5 xcexcm and not larger than the length of the aperture or less is provided. By setting the length of the pattern as above, it is possible to stably perform the fine distance measurement with high precision without reducing the aperture ratio.
According to the present invention, a manufacturing method for manufacturing an IPS mode active matrix type liquid crystal display device, which includes at least an active element substrate, an opposing substrate, a liquid crystal layer held between the active element substrate and the opposing substrate, the opposing substrate including a color layer and a black matrix layer, the active element substrate including a TFT having a gate electrode, a drain electrode and a source electrode, a pixel electrode corresponding to a pixel to be displayed, a common electrode supplied with a reference potential, a data line, a scanning line, a common electrode wiring, a data line terminal, a scanning line terminal and a common electrode wiring terminal, the common electrode wiring and the scanning line being formed of the same material in the same step, the gate electrode, the drain electrode, the source electrode of the TFT and the common electrode being electrically connected to the scanning line, the data line, the pixel electrode and the common electrode wiring, respectively, a display being performed by rotating molecular axis of the liquid crystal layer in a plane parallel to a main surface of the active element substrate by electric field applied between the pixel electrode and the common electrode substantially in parallel to the main surface of the active element substrate, is provided. In the manufacturing method of the present invention, a pattern formation of at least a display region is performed by a division exposure by using a divided photo mask and an exposure correction in patterning a new layer of a lamination of a plurality of layers, in which the common electrode wiring is formed by photolithography, is performed by a fine measurement of a relative position to the common electrode wiring layer by using a protruded or recessed portion of the common electrode wiring or at least one floating film in the same layer as that of the common electrode wiring layer.
By using the above mentioned method, it is possible to manufacture an IPS mode liquid crystal display device having high aperture ratio without unevenness of division.
With the above mentioned construction, the object of the present invention, that is, to provide an IPS mode liquid crystal display device, which has improved aperture ratio and can prevent the unevenness of display such as unevenness of division, etc., without increasing the manufacturing cost, can be achieved.